[Insight-developers] writing an ImageToImageFilter, problem with Requested Region...

[kent williams]

I've been working on an ITK filter that encapsulates some processing
previously done in an ad hoc function -- the idea being we'd like to be able
to stick it in a pipeline, rather than run one pipeline, call the function,
and run the rest of the pipeline.

The filter as I've written it works fine.  But if I try and re-use the
filter it throws an exception:

terminate called after throwing an instance of
'itk::InvalidRequestedRegionError'
  what():  
/scratch/kent/BT/BRAINS-COMPILE/Darwin/DEBUG_64-lib/Insight/Code/Common/itkD
ataObject.cxx:397:
Requested region is (at least partially) outside the largest possible
region.

In other words what I'm doing is this:

    itk::MyFilter::Pointer x = itk::MyFilter::New();
    x->SetInput(inputImage1);
    x->Update();
    firstresult = x->GetOutput();
    x->SetInput(inputImage2);
    x->Update();  // *** EXCEPTION HERE
    secondresult = x->GetOutput();

The problem happens in itk::DataObject::PropogateRequestedRegion, because
VerifyRequestedRegion() fails -- the requested region is based on the size
of inputImage1. inputImage2 has a smaller volume, so it can't satisfy the
larger RequestedRegion.

So the question is this:  What should I be doing in my filter to support
re-use?  How am I supposed to make the filter re-compute the requested
region based on the size of the new Input?

Or I guess another question might be this: Do ITK Filters, in general, ever
support this kind of re-use?